1. Field of the Invention
The present invention relates to substrate fabrication for a Liquid Crystal Display (LCD). More specifically, this invention relates to fabricating, on a common substrate, LCD transistor array substrates for LCD devices that differ in size.
2. Description of the Background Art
A liquid crystal display device includes a thin film transistor (TFT) array substrate and a liquid crystal panel including a color filter substrate facing the TFT array substrate. The TFT array substrate includes gate lines arranged in parallel in a column direction, data lines crossing the gate lines at right angles to form a matrix, thin film switching transistors formed proximate to intersections of each gate line and data line, and pixel electrodes that apply electric fields to the liquid crystal when a data signal is applied from a data line through a drain electrode of the TFT.
The color filter substrate includes: a black matrix that blocks peripheral light generated by the back light, a color filter including color resins of red, green and blue colors for realizing the pixel colors; and a common electrode for applying an electric field in concert with the pixel electrodes on the TFT array substrate to selectively orient the liquid crystal. The liquid crystal is filled between the color filter substrate and the TFT array substrate.
Typically, the liquid crystal display (LCD) panel is manufactured by separately fabricating the TFT array substrate and the color filter substrate and subsequently attaching the two substrates together. Liquid crystal is then filled between the color filter substrate and the TFT array substrate to form the LCD panel of the LCD device.
As described above, the color filter substrate and the TFT array substrate of the LCD device are fabricated on different processing lines. There is a wide variance in the size and shape of LCD panels needed for LCD devices. As a result, there is a significant number of differently sized color filter substrates and TFT array substrates that a manufacturer may be need in order to produce complete LCD panels for many different products.
Generally, the TFT array substrate and the color filter substrate are each fabricated on a glass substrate. With regard to the TFT array substrate, the glass substrate on which the TFT array substrate is formed is commonly much larger than any particular TFT array substrate for any particular LCD device. As a result, multiple TFT array substrates are fabricated at different locations on the common glass substrate. Each TFT array substrate may have the same size, and be destined for the same type of LCD device (e.g., a portable phone), or the TFT array substrates may vary in size and shape and be destined for multiple different types of LCD devices.
FIG. 1 shows an example in which a common glass substrate 101 is used to fabricate multiple TFT array substrates 102. Each TFT array substrate 102 has the same size. Because each TFT array substrate 102 has the same size, a common set of masks may be used to fabricate the TFT array substrates 102. As a result, all of the TFT array substrates 102 may be fabricated under the same fabrication conditions, have the same properties, be tested in a common manner, and thereby allow efficient mass production.
An overall summary of producing TFT array substrates on a common glass substrate is presented next. First, the fabrication areas are assigned for the TFT array substrates, typically to form as many TFT array substrates as possible on a single common glass substrate. Subsequently, gate lines are fabricated where desired in the fabrication areas, along with TFT switching devices, signal lines, and supporting structure. Next, an insulating passivation layer is applied over the entire glass substrate and the pixel electrodes are formed.
After forming the pixel electrodes, an alignment layer for free alignment of the liquid crystal is formed on the glass substrate. A rubbing process may then be carried out, for example, by rubbing the alignment layer with a cloth. After the rubbing process, a seal pattern is printed on an outer portion of an active area of each unit TFT array substrate. The seal patterns individually seal the unit TFT array substrates to color filter substrates.
The seal pattern is generally formed by a screen mask method. This method prints the seal pattern using a screen on which the seal pattern is formed. The seal pattern may also by formed using a dispenser method that draws the seal pattern with a dispenser delivering the sealant.
The screen mask method is useful for mass production, but has the disadvantage that it is susceptible to alignment errors due to contact between the seal pattern screen and an alignment layer on each TFT array substrate. On the contrary, the sealant dispenser method has the advantage of precise seal pattern, but is less suitable for mass production due to its relatively slower speed.
In addition, spacers are scattered onto each TFT array substrate. The spacers maintain a pre-selected separation between the TFT array substrates and the color filter substrates (when they are attached) The color filter substrates, also supported on a common glass substrate but prepared by a different fabrication process are then sealed to the TFT array substrates using the seal pattern. Heat and pressure are applied to bond the color filter substrates to the TFT array substrates.
Subsequently, individual unit LCD panels are cut apart, and the liquid crystal is injected into each LCD panel through an injection hole. The injection hole is sealed afterward to complete the fabrication of the LCD panel for the LCD device.
In the processes described above, the common glass substrate was used to produce multiple identical LCD panels. As a result, all components of the TFT array substrates formed on common glass substrate have same manufacturing standards and characteristics.
However, when the common glass substrate is used to manufacture TFT array substrates that differ in size and shape, then the resultant LCD panels, and their underlying components, will adhere to differing manufacturing standards and characteristics. The common glass substrate is sometimes used in this manner because the common glass substrate is not always an integral multiple of a certain TFT array substrate size. Thus, to more efficiently use the glass substrate, it may be desirable to fill what would be unused area with TFT array substrates of other sizes.
For example, the common glass substrate may be employed to manufacture both an 8-inch LCD panel and a 14-inch LCD panel. In that case, the TFT channels in each TFT array substrate are manufactured with different masks and therefore adhere to different manufacturing standards and device characteristics. As a result, quality control (e.g., performance testing) for each different LCD panel must be carried out independently. Independent testing, however, increases the cost and time required to exercise quality control, and thus frustrates mass production. Furthermore, an improvement developed for fabricating a particular TFT (e.g., an improvement in channel performance) generally cannot be applied to other TFTs for different TFT array substrates.
As a result, it has been very complex to fabricate TFT array substrates for different LCD panels on a common glass substrate. In part, the complexity is due to applying different mask processes for each different TFT array substrate. For example, the TFTs incorporated in the 14-inch LCD panel are fabricated using a different mask set than the TFTs incorporated into the 8-inch LCD panel. Inferiorities are easily generated, and yield commonly decreases.
There is a need for addressing the problems noted above, and others previously experienced.